I just previously highlighted the same highlighting that you did. Mueller can't be appointed by an Asst AG.Here's the text of the appointments clause. I think you missed some important details, that I've highlighted for you.
... and [the President] shall nominate, and by and with the Advice and Consent of the Senate, shall appoint Ambassadors, other public Ministers and Consuls, Judges of the supreme Court, and all other Officers of the United States, whose Appointments are not herein otherwise provided for, and which shall be established by Law: but the Congress may by Law vest the Appointment of such inferior Officers, as they think proper, in the President alone, in the Courts of Law, or in the Heads of Departments.
Sure he can - since Congress has vested the power to appoint "such inferior officers" in the Attorney General (or Acting AG, in cases of recusal). I don't know why you're not wrapping your head around this.